Fine metal oxide powder having high dispersibility and toner composition comprising the same

ABSTRACT

Regarding the metal oxide fine powder, which is used as the additive of a powder material and is hydrophobic treated on the surface, the peak of the particle size distribution of the agglomerated particle is made to be less than the same level of average size of the powder material, so that said powder has high dispersibility in the powder material. When this metal oxide fine powder is used as the external additive, such as the toner for the, electronic photograph, the standup of the electrostatic charge, the image quality, and the cleaning characteristic are improved remarkably.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a high dispersible metal oxidefine powder added in a powder material, such as a coating powder, atoner for an electronic photograph, etc., for the purpose, such asflowability improve, caking prevention, and electrostatic charge controlof a powder, and its composite. Specifically, the present inventionrelates to a high dispersible metal oxide fine powder, which canremarkably improve standup of the electrostatic charge, a image quality,and a cleaning characteristic, by containing said metal oxide finepowder, and to a toner composite containing said powder. In addition,the toner composite of the present invention contains the powder, whichis used for not only the electronic photograph but also variouselectrostatic pictures, such as an electrostatic recording, anelectrostatic printing, etc.

BACKGROUND OF THE INVENTION

[0002] A developer of the electronic photograph, etc., has comprised thetoner composite, in which some external additives are added to thetoner, and contained a carrier, for example, a glass bead, an ironpowder, or an ferrite carrier, etc., if necessary. As the toner of theexternal additive, the fine powders are used, which are surface-treatedon the metal oxide fine powder, such as fine silica, titania, oralumina, etc., with an organic material, and the flowability and theelectrostatic charge of the toner are controlled by this externaladditive. Especially, the average particle size of the toner has beenmade fine from about 10 μm to 5 μm recently because of the demand ofhigh imaging quality of the electronic photograph. However, there is aproblem with this making fine powder, in which the flowability of thetoner is decreased, so that is a tendency that the amount of theexternal additive is increased to improve the flowability of the toner.Moreover, a characteristic of the external additive has been muchinfluenced on the electrostatic charge of the toner by increasing saidamount of the additive. For example, if the additive is distributedirregularly in the toner, a high quality development characteristic cannot be obtained. For this reason, the additive having gooddispersibility is required.

[0003] Conventionally, as the external additives of the toner for theelectronic photograph, the metal oxide fine powder treated withhydrophobic treatment is used. When the amount of the treatment reagentused is increased to stabilize the surface treatment, it becomesagglomerated the particle, so that the flowability and thedispersibility are decreased on the contrary. Therefore, the process ofpulverizing the surface-treated metal oxide powder is proposed. Forexample, in Japanese Patent Raid Open Hei 2-42452, or Hei 8-152742, thepulverizing to use the surface-treated metal oxide fine powder by a jetmill is shown. However, this pulverizing by the jet mill has high energycost and, moreover, the particle size after pulverizing is very fine, sothat there are problems in dust and handling.

DISCLOSURE OF THE INVENTION

[0004] The present invention solves the conventional above-mentionedproblems about the metal oxide fine powder used as the external additiveof the powder material, such as the toner, etc., and provides the metaloxide fine powder, which has low pulverizing cost, good dispersibilityat the time of adding to the powder material, by using the metal oxidefine powder controlled the distribution of the agglomerated particlesize according to the average particle size of the powder material, suchas the toner etc. Moreover, the present invention also provides thetoner composite having the stable electrostatic charge and the goodflowability, by containing this metal oxide fine powder.

[0005] That is, the present invention relates to the metal oxide finepowder used as the external additive of the powder material, wherein thesurface of said powder is hydrophobic treated and has highdispersibility in the powder material by which the peak of the sizedistribution of the agglomerated particles makes lower than the level ofthe average particle size of the powder material. Regarding the metaloxide fine powder of the present invention, for example, it ispreferable that the average first particle size is less than 300 nm(nano meter), its agglomerated particle has the peak of the particlesize distribution in the range of less than 10 μm (micron meter)preferably 5 μm, the specific surface area by the BET method is 10-400m²/g, the hydrophobicity is more than 30%, and the bulk density is morethan 30 g/L, preferably more than 100 g/L. Moreover, the composition ofthe metal oxide fine powder is, for example, silica, titania, alumina,zirconia, or these composite oxides, which are hydrophobic treated onthe surface with organic silicon compounds. Moreover, the powdermaterial added the metal oxide fine powder of the present invention is,for example, the toner for the powder coating or the electronicphotograph. Furthermore, the present invention also relates to the tonercomposite, which has high flowability by addition with such metal oxidefine powder. It is preferable that the content of the metal oxide finepowder in this toner composite is 0.01-5.0% by weight.

[0006] [I] Metal Oxide Fine Powder

[0007] The metal oxide fine powder of the present invention is the finepowder, which is silica, titania, alumina, zirconia, a composite oxideof more than two kinds of these metals, or a mixed oxide of more thantwo kinds of metal oxides. In addition, in the present invention, silicais also included in the metal oxide. The metal oxide fine powder of thepresent invention is obtained by the surface-treatment with the organicsilicon compound, etc., and pulverizing. Furthermore, it is availablethat the surface treatment and the pulverizing are done simultaneously,before or after.

[0008] [II] Surface Treatment

[0009] The above-mentioned metal oxide fine powder is hydrophobictreated with the surface treatment reagents, such as the organic siliconcompounds. As these surface treatment reagent s, for example, a siliconeoil or a silane coupling reagent, such as trimethylchlorosilane,dimethyldichlorosilane, methyltrichlorosilane, trimethylalkoxisilane,dimethylalkoxisilane, methyltrialkoxysilane, and hexamethyldisilazane,etc., an organopolysiloxane or some modified silicone oil including anorganopolysiloxane are used. The kind of these silane coupling reagentsis not limited, and various kinds of alkoxysilane, chlorosilane, orsilazane can be used. Moreover, the kind of the organopolysiloxane isnot also limited, so that a dimethyl silicone oil, a methylhydrogenesilicone oil, a phenyl silicone oil, a non-reactive silicone oil, or areactive silicone oil, can be used.

[0010] The process and conditions of the surface treatment are notlimited. It is available that the conventional surface treatment processis done. For example, an uniform surface modified metal oxide finepowder is obtained by the followings. At first, predetermined amount ofthe silane coupling agent or the organopolysiloxane is dropped orsprayed onto the metal oxide powder to be dispersed fully with a solventif necessary. The dispersed powder is stirred at more than 50° C.,preferably more than 100° C., more preferably 100° C.-400° C. for 0.1-5hours, preferably 1-2 hours, and then is cooled.

[0011] [III] Hydrophobicity

[0012] Regarding the surface treated metal oxide fine powder, it ispreferably that the degree of hydrophobicity measured by a transparencymethod is more than 30%. If the hydrophobicity is less than 30%, theimprovement of the moisture resistance or the electrostatic chargestability of the toner is not sufficient when it is used as the externaladditive of the toner. It is more preferably that the hydrophobicity ismore than 60%.

[0013] [IV] Particle Size Range

[0014] The surface modified metal oxide fine powder of the presentinvention is used as the external additive of the powder material,wherein the peak of the particle size distribution of the agglomeratedparticle (the secondary particle) is less than the same level of theaverage particle size of the above-mentioned powder material. It ispreferably that said metal oxide fine powder has less than 300 nm (nanometer) of the average primary particle size, 10-400 m²/g of the specificsurface area by the BET method and the agglomerated particle has thepeak of the particle size distribution at the range less than 10 μm(micro meter) preferably less than 5 μm. In this case, the meaning ofthe powder material is the powder added the metal oxide particle of thepresent invention, such as the toner for the electronic photograph etc.The meaning of less than the same level of the average particle size ofthe powder material is same or less than the average particle size ofthe powder material. Moreover, the meaning of having the peak of theparticle size distribution is that having the maximum value in thevolume distribution curve of the particle size. In addition, the meaningof the peak of less than 10 μm is that the maximum value of the particlesize distribution is in the range of less than 10 μm. When there aremultiple peaks, the meaning of the peak of less than 10 μm is that thebiggest maximum value of them is in the range of less than 10 μm. It ismore preferably that the fine metal oxide powder of this invention hasthe peak of the particle size distribution in the particle size range of0.1-10 μm, wherein the agglomerated particles, which are more than 55%of a whole volume, are included.

[0015] Regarding the toner for the electronic photograph, although thetoner having the average particle, size of about 10 μm has been used ingeneral, it is in the tendency that, more fine toner having the averageparticle size of about 5 μm is used for high image quality. Therefore,in the present invention, the particle size of the agglomerated particleof the metal oxide fine powder is made to have the peak of the particlesize distribution at less than 10 μm, preferably less than 5 μm, to befine as the same size or less than the size of the toner. By this way,the agglomerated particle of the metal oxide fine powder can existbetween the toner particles, so that the caking between the tonerparticles is prevented to increase the flowability of the tonercomposite. When the distribution peak of these agglomerated particles isin the range of more than 10 μm, the metal oxide particle cannot existbetween the toner particles, which have smaller size than this value, sothat the flowability of the toner composite cannot be improved. Inaddition, since the metal oxide fine powder exists in the agglomeratedstate in general, when the powder, in which the primary particle size issmaller than the toner particle, is used, the sufficient effect for theflowability improve can not be acquired without controlling the particlesize of the agglomerated particle. Moreover, when the average particlesize of the primary particle is more than 300 nm, or the specificsurface area of the primary particle is smaller than 10 m²/g by the BETmethod, it is not preferably since the distribution peak of theagglomerated particles is easy to be in the range of more than 10 μm. Onthe other hand, when the specific surface area is more than 400 m²/g bythe BET method, it is not preferably since the caking is too strong tobecome the peak of the particle size distribution more than 10 μm.

[0016] [V] Pulverizing/Pulverizing Process

[0017] The metal oxide fine powder hydrophobic treated on the surface ispulverized or pulverizing processed to be prepared to theabove-mentioned particle size range. It is available that thispulverizing or pulverizing process is same as the conventional one. Inaddition, by processing to combine the pulverizing or the pulverizingprocess and the classification, the metal oxide fine powder having theabove-mentioned particle size can be obtained efficiently. As apulverizing machine, a mechanical pulverizing machines, such as apin-mill, a fine-mill, a bead-mill, a ball-mill, a hummer-mill, or achopper, etc., can be used. As the classification process, an airclassification, a sieving, or a jet sieving, etc., can be used. Inaddition, the actual conditions for controlling to the above-mentionedparticle size range are determined according to the kinds of the metaloxide materials, the conditions of the surface modification, thepulverizing equipments, or the classification equipments. Regarding thesurface treated metal oxide powder, the agglomerated particles of saidpowder become to the agglomerates, in which said particles combine morelike a net, and, furthermore, these agglomerate combine to exist as theclusters. These agglomerates or clusters are pulverized to the level ofthe agglomerated particle or the primary particle by the pulverizingprocess.

[0018] [VI] Bulk Density

[0019] Regarding the metal oxide fine powder of the present invention,it is preferably that the bulk density is more than 30 g/L, morepreferably more than 100 g/L. When the bulk density is less than 30 g/L,there are problems in dust, and handling of transportation, etc. Whenthe bulk density is more than 100 g/L, the handling is good, and thedispersibility is improved remarkably at the time of adding to thepowder. Furthermore, it is easy to control the distribution peak of theparticle size.

[0020] [VII] Toner Composite

[0021] The toner composite for the electronic photograph etc. of thepresent invention contains the above-mentioned metal oxide fine powderhaving the high dispersibility. By containing the metal oxide finepowder having the high dispersibility, where the particle size of theagglomerated particle is controlled as above-mentioned particle size,said metal oxide fine powder is dispersed uniformly between the tonerparticles, so that it is obtained that the toner composite has the highelectrostatic charge stability and the excellent flowability. Althoughthe content of the above-mentioned metal oxide fine powder in the tonercomposite is based on the kinds of the metal oxide and thehydrophobicity of the powder etc., it is preferably that the content is0.01-5.0% by weight in general. When the content is less than 0.01% byweight, the effect of addition is not acquired sufficiently. On theother hand, when the addition is more than 5.0% by weight, there is nowide difference of the flowability or the electrostatic chargestability, and there may be a problem in the image quality or thecleaning.

[0022] It is available that the composition of the toner composite ofthe present invention is same as the conventional composition exceptingthe above-mentioned metal oxide fine powder. For example, as the toner,the common used toner can be used, which is made by blending coatings,and additives, with the binder resin, i.e. the thermoplastic resin. Asthe additives, magnetic materials, or electrostatic charge controlreagents are used if necessary. Moreover, it is available that saidtoner is used magnetic type or non-magnetic type, negative or positivecharge, and monochrome or color. In addition, it is also available thatsaid toner can be used as the mono component system not using a career,or the two components system using a career. In addition, in the tonercomposite of the present invention for the electronic photograph etc.,the above-mentioned metal oxide fine powder used as the externaladditive can be not only used individually, but also used together withthe other metal oxide fine powder. For example, the above-mentionedmetal oxide fine powder can be used together with the fine silica powderproduced by dry-process, the fine titanium oxide powder produced bydry-process, and the fine titanium oxide powder produced by wet-process,etc., which are surface-modified by other processes.

EXAMPLE AND COMPARISON EXAMPLE

[0023] The invention will be explained more concretely with followingexamples. In addition, in the following examples, the particle sizedistribution, the hydrophobicity, the flowability, the electrostaticcharge and its stability, and the image qualities, were measured andevaluated as follows.

[0024] (A) Particle Size Distribution

[0025] The particle size distribution with the volume standard wasmeasured by the particle size distribution measuring equipment by laserdiffraction/dispersion method (LA-910 made by Horiba Co. LTD).

[0026] (B) Hydrophobicity

[0027] 1 g of sample was weighed and taken into the 200 ml of separatoryfunnel, and 100 ml of pure water was added to said funnel. And aftermixing for 10 minutes by the tumbler mixer, the mixed substance was putquietly for 10 minutes. After that, 20-30 ml of the solution was drawnout from the under layer, and 10 ml of said solution was taken out to aquartz cell. The solution was measured by a spectrophotometer using purewater as a blank. The transparency of 500 nm wavelength of light wasdefined as the hydrophobicity.

[0028] (C) Flowability

[0029] 0.4 g of the metal oxide fine powder and 40 g of the tonerparticle (the average particle diameter of 7 μm), were stirred and mixedby the mixer to prepare the toner composite for the electronicphotograph. In addition, the mixed substance was screened out in orderthrough the three sorts of screens, i.e., 150 μm, 75 μm and 45 μm, byvibrating, in use of a powder tester (PT-N type made by HOSOKAWA MICRONCo. LTD), and the ratio of the powder passing all screens was defined asthe ratio of 45 μm screen passage. In these values, more than 80% ofthis value was defined as good flowability.

[0030] (D) Electrostatic Charge

[0031] 50 g of an iron powder career and 0.1 g of the high dispersiblehydrophobic metal oxide fine powder were put into a glass containerhaving 75 ml of volume, and after mixing these powders for 5 minutes bya tumbler mixer, 0.1 g of the mixed powder of this metal oxide finepowder and the iron powder were extracted. Then, the measured valueafter blowing with nitrogen gas for 1 minute by using the measuringequipment of blow-off electrostatic charge (TB-200 type made by ToshibaChemical CORP), was defined as the electrostatic charge.

[0032] (E) Electrostatic Charge Stability

[0033] 0.4 g of the metal oxide fine powder and 40 g of the tonerparticle having 7 μm diameter were put into the glass container having75 ml of volume and mixed by stirring with the mixer to prepare thetoner composite for the electronic photograph. The mixed powder, inwhich 48 g of the iron powder career was added to 2 g of this tonercomposite, was kept for 24 hours under the conditions of hightemperature and high humidity (hereinafter said to as HH condition), andlow temperature and low humidity (hereinafter said to as LL condition).In addition, HH condition is temperature of 40° C. and humidity of 85%,and LL condition is temperature of 10° C. and humidity of 20%. Afterthese treatments, this mixed powder was mixed for 5 minutes by thetumbler mixer and 0.2 g of the mixed powder was extracted to measure theelectrostatic charge. The electrostatic charge was measured afterblowing nitrogen gas for 1 minute by using the measuring equipment ofblow-off electrostatic charge (TB-200 type made by Toshiba ChemicalCORP), and the difference between the electrostatic charge of thepowders under HH condition and LL condition, was obtained. When thisdifference is less than 5 μC/g, the powder was defined to be stable tothe ambient variation.

[0034] (F) Image Quality

[0035] When more than 50,000 sheets were printed by using a commercialcopying machine, the picture fogs and the distribution of image densitywere checked.

Example 1

[0036] 100 weight parts of fumed-silica (made by NIPPON AEROSIL Co.,LTD. and the specific surface area of 400 m²/g and the average diameterof the primary particle of about 7 nm) was put into the mixer, and whilestirring under nitrogen atmosphere, 35 weight parts of theorganopolysiloxane and 65 weight parts of the normal-hexane were droppedon the mixed powder to heat at 250° C. for 1 hour. After removing thesolvent, the mixed substance was pulverized and classified to be cooled.The particle size distribution of the obtained fine powder by the laserdiffraction, had the peak at 0.25 μm and 70% of the agglomeratedparticles in the whole volume were contained in the range of 0.1-10 μmIn addition, in said obtained fine powder, the hydrophobicity was 96% bythe transparency method, the specific surface area was 150 m²/g by theBET method, pH was 5.7, and the bulk density was 30 g/l. This finepowder was mixed to the negative charge toner, which has 7 μm of averageparticle diameter, to prepare the toner composite. When this flowabilitywas measured, the ratio of 45 μm screen passage was 85%, the angle ofrest was 32 degrees, so that good flowability was obtained. Moreover,the difference of the electrostatic charge was 2 μC/g by theelectrostatic charge stability measurement, and this value was goodelectrostatic charge stability. In addition, when more than 50,000sheets were copied using said toner composite by the commercial copyingmachine, the picture fogs and the difference of the image density didnot appear and was good image quality.

Comparison Example 1

[0037] The hydrophobic silica fine powder was made by the same processas Example 1 excepting pulverizing and classifying by the fine-mill. Theparticle size distribution of the obtained fine powder had the peak at30 μm by the laser diffraction, and the hydrophobicity was 90% by thetransparency method, the specific surface area was 150 m²/g, pH was 5.5,and the bulk density was 61 g/l. This fine powder was mixed to the tonerof the negative charge having 7 μm of the average particle size toprepare the toner composite. When the flowability was measured, theratio of 45 μm screen passage was 70%, and the angle of rest was 40degrees. In addition, the difference of the electrostatic charge was 10μC/g by the electrostatic charge stability measurement, and the chargevariation was large. Furthermore, when 2,000 sheets were copied by thecommercial copying machine, the white spots appeared and there was aproblem in the image quality.

Example 2

[0038] 100 weight parts of an ultra-fine titania powder (made by NIPPONNAEROSIL CO., LTD. titanium oxide TN20, in which the specific surfacearea of 20 m²/g) was put into the mixer, and while stirring undernitrogen atmosphere, 4 weight parts of octyltrimethoxysilane (made bySINETSU KAGAKU CO., LTD, KBM3083), and 16 weight parts of methanol weredropped on the mixed powder. After heating and stirring at 150° C. for 1hour, the solvent was removed and the mixed substance was pulverized andclassified by using the pin-mill and an air classification machine to becooled. The particle size distribution of the obtained fine powder hadthe distribution peak of the agglomerated particle at 3.5 μm by thelaser diffraction. In addition, in said obtained fine powder, thehydrophobicity was 92.2% by the transparency method, the specificsurface area was 13 m²/g, pH was 4.3, and bulk density was 45 g/l. Thisfine powder was mixed to the negative charge toner having 7 μm of theaverage particle size to prepare the toner composite. When thisflowability was measured, the ratio of the 45 μm screen passage was 80%,and the angle of rest was 40 degrees, so that the good flowability wasobtained. Moreover, the difference of the electrostatic charge was 4μC/g by the electrostatic charge stability measurement, and it was goodelectrostatic charge stability. Furthermore, when more than 50,000sheets were copied using the above-mentioned toner composite by thecommercial copying machine, the image quality was good.

Comparison Example 2

[0039] The hydrophobic titania fine powder was made by the same processas Example 2 excepting pulverizing and classifying. The particle sizedistribution of the obtained fine powder had the peak at 50 μm. Inaddition, in said obtained powder, the hydrophobicity was 70% by thetransparency method, the specific surface area was 12 m²/g by the BETmethod, pH was 4.4, and the bulk density was 85 g/l. This fine powderwas mixed to the negative charge toner having 7 μm of the averageparticle size to prepare the toner composite. When this flowability wasmeasured, the ratio of the 45 μm screen passage was 50%, and the angleof rest was 47 degrees. Moreover, the difference of the electrostaticcharge was 8 μC/g by the electrostatic charge stability measurement, sothat electrostatic charge variation was large. Furthermore, when 1,000sheets were copied by the commercial copying machine, the fogs appearedand there was a problem in the image quality.

Example 3

[0040] 100 weight parts of an ultra-fine of alumina powder (made byDEGUSAHYUELUS Company, A1203-C having the specific surface area of 100m2/g) was put into the mixer, and while stirring under nitrogenatmosphere, 20 weight parts of the organopolysiloxane and 40 weightparts of the normal-hexane were dropped on said mixed powder. And afterstirring for 1 hour at 250° C., and removing the solvent, said stirredsubstance was pulverizing by the ball-mill to be classified by the jetsheave, and was cooled. The particle size distribution of the obtainedfine powder had the distribution peak of the agglomerated particle at3.0 μm by the laser diffraction. In addition, in said obtained powder,the hydrophobicity was 63% by the transparency method, the specificsurface area was 62 m²/g by the BET method, pH was 5.4, and the bulkdensity was 130 g/l. This fine powder was mixed to the negative chargetoner having 7 μm of the average particle diameter to prepare the tonercomposite. When the flowability was measured, the ratio of 45 μm screenpassage was 88%, and the angle of rest was 38 degrees, so that it wasgood flowability. Moreover, the difference of the electrostatic chargewas 3 μC/g by the electrostatic charge stability measurement, and it wasgood electrostatic charge stability. Furthermore, when more than 5000sheets were copied using the above-mentioned toner composite by thecommercial copying machine, the image quality was good.

Comparison Example 3

[0041] The hydrophobic alumina fine powder was made by the same processas Example 3 excepting pulverizing and classifying. The particle sizedistribution of said fine powder had the distribution peak of theagglomerated particle at 25.0 μm by the laser diffraction. In addition,in said obtained powder, the hydrophobicity was 40% by the transparencymethod, the specific surface area was 58 m²/g by the BET method, pH was5.5, and the bulk density was 60 g/l. This fine powder was mixed to thenegative charge toner having 7 μm of the average particle size toprepare the toner composite. When the flowability was measured, theratio of 45 μm screen passage was 68%, and the angle of rest was 48degrees. Moreover, the difference of the electrostatic charge was 8 μC/gby the electrostatic charge stability measurement, and the electrostaticcharge variation was large. Furthermore, when 3000 sheets were copiedusing the above-mentioned toner composite by the commercial copyingmachine, the fogs appeared, and there was a problem in the imagequality.

Example 4

[0042] 100 weight parts of a hydrophobic fumed-silica (made by NIPPONAEROSIL CO., LTD, Aerosil R 972, the specific surface area is 120 m²/g)was put into the mixer, and while stirring by using a chopperpulverizing under nitrogen atmosphere, 13 weight parts of amino-modifiedsilicone oil (made by SINETSU KAGAGU CO., LTD, KF393), and 40 weightparts of the normal-hexane were dropped on said mixer. After heating andstirring at 200° C. for 1 hour, and removing the solvent, said stirredsubstance was classified by the air current classification machine to becooled. The particle size distribution of the obtained fine powder hadthe peak at 9.0 μm by the laser diffraction. In addition, in saidobtained powder, the hydrophobicity was 82% by the transparency method,the specific surface area was 70 m²/g by the BET method, pH was 8.3, andthe bulk density was 33 g/l. This fine powder is mixed to the positivecharge toner having 7 μm of the average particle size to prepare thetoner composite. In addition, when the flowability was measured, theratio of 45 μm screen passage was 88%, and the angle of rest was 32degrees, and it was good flowability. Moreover, the difference of theelectrostatic charge was 5 μC/g by the electrostatic charge stabilitymeasurement, and it was good electrostatic charge stability.Furthermore, when more than 50000 sheets were copied using theabove-mentioned toner composite by the commercial copying machine, theimage quality was good.

Comparison Example 4

[0043] The hydrophobic silica fine powder was made by the same processas Example 4 excepting pulverizing and classifying. The particle sizedistribution of the obtained fine powder had the peak at 47 μm, wherethe hydrophobicity was 80% by the transparency method, the specificsurface area was 65 m²/g, pH was 8.2, and the bulk density was 54 g/l.This powder was mixed to the positive charge toner having 7 μm of theaverage particle diameter to prepare the toner composite. In addition,when the flowability was measured, the ratio of the 45 μm screen passagewas 65%, and the angle of rest was 39 degrees. Moreover, the differenceof the electrostatic charge was 12 μC/g by the electrostatic chargestability measurement, and the electrostatic charge variation was large.Furthermore, when 1000 sheets were copied using the above-mentionedtoner composite by the commercial copying machine, the pictureconcentration became thin, and there was a problem in the image quality.

[0044] The above results are shown in Table 1 and Table 2. As shown inthis results, in the case of the fine powder, which was pulverized andclassified at least more than one time, simultaneously, before or after,with the surface modification, and has the controlled maximum peak ofthe agglomerated particle size (volume standard) of less than 10 um,preferably less than 5 um, the flowability of the toner composite andthe electrostatic charge stability are improved remarkably. In addition,said powder has good picture reproducible characteristics. TABLE 1Characteristics of metal oxide fine powders and the toner compositeusing them Example 1 Example 2 Example 3 Example 4 Kinds of oxide SilicaTitania Alumina Silica Pulverizing method Fine mill Pin-mill Ball-millChopper Classification Air Jet-sieve Air method classificationclassification Peak (μm) 0.25 3.5 3.0 9.0 (0.1˜10) Hydrophobicity (%) 9692.2 63 82 Specific surface area 150 13 62 70 by the BET method (m²/g)pH 5.7 4.3 5.4 8.3 Bulk density (g/l) 30 45 130 33 Flowability ◯ ◯ ◯ ◯Electrostatic charge ◯ ◯ ◯ ◯ Image quality ◯ ◯ ◯ ◯

[0045] TABLE 2 Characteristics of metal oxide fine powders and the tonercomposite using them Comparison Comparison Comparison Comparison Example1 Example 2 Example 3 Example 4 Oxide Silica Titania Alumina SilicaPulverizing and No No No No Classification pulverizing pulverizingpulverizing pulverizing and and and and classification classificationclassification classification Peak (μm) 30 50 25 47 Hydrophobicity 90 7040 80 (%) Specific 150 12 58 65 surface area by the BET method (m²/g) pH5.5 4.4 5.5 8.2 Bulk density 61 85 60 54 (g/l) Flowability Δ X Δ ΔElectrostatic X X X X charge Image quality X X X X

EFFECTIVENESS OF THE INVENTION

[0046] The hydrophobic metal oxide fine powder having highdispersibility of the present invention can be dispersed in the tonereasily, and improve the electrostatic charge and the flowability of thetoner with balance sufficiently. That is, the stable electrostaticcharge, which is not influenced by the environmental conditions, such ashumidity or temperature, and also with time, is realized, and theflowability is improved, by adding the hydrophobic metal oxide finepowder having high dispersiibility of the present invention to thetoner. For this reason, by using said powder for the developer of theelectronic photograph etc., when the copies having large number arerepeated, the good image quality reproducibility is maintained.

What is claimed is:
 1. (after amendment) a metal oxide fine powder having high dispersibility in a powder material, which is hydrophobic-treated on the surface and used as an additive of the powder material, wherein, a primary particle of said powder having the average size of less than 300 nm (nano meter) and the specific surface area of 10-400 m²/g by the bet method is hydrophobic-treated to have the hydrophobicity of more than 30%, and said hydrophobic-treated powder is pulverized or pulverizing processed to have a peak of a particle size distribution containing more than 55% of agglomerated particles and being in the range of 0.1 to 10 μm.
 2. (After amendment) The metal oxide fine powder according to claim 1, wherein, the peak of the particle size distribution of the agglomerated particles is less than the same level of the average particle size of the powder material.
 3. (After amendment) The metal oxide fine powder according to claim 1, wherein, the peak of the particle size distribution of the agglomerated particles is in the range of less than 5 μm (micron).
 4. (Deleted)
 5. (Deleted)
 6. (After amendment) The metal oxide fine powder according to any one of claim 1 or 3, wherein the bulk density is more than 30 g/L.
 7. (After amendment) The metal oxide fine powder according to claim 6, wherein the bulk density is more than 100 g/L.
 8. (After amendment) The metal oxide fine powder according to any one of claims 1, 3, 6 or 7, wherein the metal oxide fine powder is silica, titania, alumina, zirconia, or a composite oxide of these oxides, which is hydrophobic treated on the surface with an organic silicon compound.
 9. (After amendment) The metal oxide fine powder according to any one of claims 1, 3, 6, 7, or 8, wherein the powder material is a toner for a powder coating or an electronic photograph.
 10. (After amendment) A toner composite, wherein the flowability is raised by adding the metal oxide fine powder according to any one of claims 1, 3, 4, 6, 7, 8, or
 9. 11. (After amendment) The toner composite according to claim 10, wherein the content of the metal oxide fine powder is 0.01 to 5.0% by weight. 